Great work on the flexi riser. I have been meaning to do a mod like this for a while, with mobo and gfx card back-to-back, but too many bad experiences I have heard about with those risers. I hope it works out for you!

Testing the ventilators of PSU.
Without 3D-load power supply still is cold, but the minimum rpm of the fans is 1500, less than this value PSU (or m/board) can't set.

DIY -rheobus.
Microcontroller, digital thermometer and some small parts...
Uses PWM for control 4-pin ventilators, all settings are made with the program.
Connect to PC via serial port (it is present on the board) or via USB/RS232-adapter.

With this device minimum rpm is 1000 (if PWM=0), and if temp of PSU still less than 30-35 celsius, the ventilators are off.

DIY -rheobus.
Microcontroller, digital thermometer and some small parts...
Uses PWM for control 4-pin ventilators, all settings are made with the program.
Connect to PC via serial port (it is present on the board) or via USB/RS232-adapter.